The invention disclosed and claimed herein relates generally to a means for converting two-dimensional mechanical motion into control signals in digital form, and relates more specifically to a cursor control for use in conjunction with a cathode ray tube (CRT) display device.
Various cursor controls or cursor manipulators have previously been developed to enable the operator of a CRT display console to control the motion of a movable light element in two spatial dimensions on a planar CRT screen, and particularly to control the direction and rate of motion, or speed, of the element with respect to horizontal and vertical axes. Two of the more recent of such devices include the track ball and the finger sweep cursor controls.
In the track ball cursor control a rotatable spherical control element is juxtaposed in cooperative relationship with certain electrical apparatus such as a series of potentiometers. Rotation of the spherical element about a reference axis incrementally changes horizontal displacement of a movable light element on a CRT, and rotation about another reference axis, orthogonal to the first, incrementally changes vertical displacement. However, the incremental displacements provided by even an entire rotation of a spherical element about either reference axis may be so slight that an operator is required to make numerous rotations to realize a desired adjustment of light element motion. Operator efficiency may thereby be significantly reduced. In addition, track balls are expensive and structurally complex, and may be readily affected by environmental conditions.
In the finger sweep cursor control, light sensing devices, or sensors, are situated in two orthogonally positioned rows within an enclosure, each light sensor receiving a beam of light from a spatially separated light source and being activated thereby to produce an output voltage. To control horizontal motion of a movable light element on a CRT screen, an operator moves or sweeps his finger along one of the sensor rows, sequentially interrupting the beams to the sensors and temporarily deactivating them. Horizontal control circuitry coupled to the outputs of the sensors responds to the sequential deactivations by incrementally displacing the light element in relation to the horizontal axis of the CRT. To incrementally displace the light element in relation to the vertical axis, the operator moves or sweeps his finger along the other sensor row, the outputs of which are similarly coupled to vertical control circuitry. The rate of motion of the light element with respect to either CRT axis is determined by the rapidity of the movement of the operator's finger along the corresponding sensor row. As with the track ball, numerous movements of an operator's hand or finger may be required to effect a single change in light element motion, reducing operator efficiency and resulting in operator fatigue. Additionally, certain persons may be unable to operate a finger sweep control due to insufficient finger dexterity or other structural limitation of their hands or fingers.